CICEET Progress Report for the period 3/15/05 Through 9/15/05

Project Title: Mitigating the effects of excess nutrients in coastal waters through bivalve aquaculture and harvesting
Principal Investigator(s): Hauke Kite-Powell, Dror Angel, Heidi Clark, Kevin Kroeger, Bill Walton, Di Jin, and Porter Hoagland Woods Hole Oceanographic Institution

Figures

Figure 1

Tables

Table 1

Model development:

• application of field work data to bio-geophysical model
• review and revision of model structure and preliminary results

Field work:

• redeployment of oysters from deep water to experiment plots, and continuation of on-bottom and cage growout experiments
• nitrogen cycling sampling and analysis

Report production and dissemination

Progress on Tasks
Application of field work data to bio-geophysical model:
Final application of field work data to the model will take place in the fall of 2005, once July 2005 field work data analysis is complete. See below for preliminary results. Review and revision of model will take place in the fall as well.

Growout experiments:
Oysters were restored to the experimental site in late April 2005. Over-winter survival was excellent, and both oysters and quahogs have grown well in the experimental plots during the 2005 summer growing season. See data below. We have separated oysters in the higher density plots (1,000 and 2,000 oysters/tray) into two stacked trays to reduce crowding.

WHOI Summer Student Fellow Jessica Bell (Wellesley College) worked with the project team during the summer of 2005, focusing on oyster growth and bio-geophysical modeling.

Nitrogen cycling sampling and analysis:
Sediment samples were taken at the experiment site in late July 2005, and are being analyzed for denitrification rates, carbon and nitrogen content, and grain size at this time.

Report production:
We have received a no-cost extension for the project and will complete report writing and dissemination activities in the winter of 2005-06.

Difficulties
None.

Preliminary Data
Oyster growth and survival
Table 1 summarizes results of shellfish growth monitoring in July 2005. These results continue to exhibit a density effect on growth rates for oysters.

Both growth and survival rates are good among oysters in the experimental plots, and suggest that oysters in the Waquoit Bay setting can be grown out to commercial market size over three growing seasons.

Bio-geophysical modeling
The final version of our bio-geophysical model will be developed with the 2005 field work data. A preliminary version, using conservative assumptions about the effect of oysters on denitrification rates in underlying sediments, suggests that oyster aquaculture is a cost-effective and potentially significant tool in the effort to manage nutrients in coastal water bodies.

For example, our preliminary estimates suggest that a commercially-structured oyster aquaculture operation, growing 500 oysters per 1-m² tray to market size over three years, will remove on average 0.41 kg N/m²-yr from the ecosystem. About half of this N removal is due to N sequestration in oyster tissue, and half is due to enhanced denitrification in sediments below the trays. Nearly 75% of final N removal is attributable to oysters in their third year of growout, because large oysters contribute more significantly to enhancement of denitrification, and because sequestered N is removed from the ecosystem at harvest time. The denitrification effects here are estimated based on estimates developed by Newell et al. (2004) in the Chesapeake; we will substitute denitrification rate measurements from Waquoit Bay once laboratory analysis of July 2005 sediment samples in complete.

N loading into Waquoit Bay is estimated to have more than doubled between 1938 and 1990, from 10,900 to 24,300 kg N/yr (Bowen and Valiela 2001). Present loading into the Head of the Bay region of Waquoit Bay, for example, is around 500 kg/yr (Valiela et al. 2000) ­ an estimated increase in N load of 275 kg/yr from 1938 levels. If, for purposes of discussion, we set as a target the elimination of 50% of this increase by shellfish aquaculture, we need to remove some 138 kg N/yr, equivalent to 340 m² of oyster aquaculture, in the Head of the Bay. This represents about 6% of the area of the Head of the Bay (57 ha), and suggests that the approach is feasible in principle.

Because shellfish aquaculture in this form is economically viable independent of its beneficial ecological effects, this suggests that it might be considered as one of the first options in efforts to manage nutrient levels. Once the potential for nutrient removal through aquaculture has been exhausted, more costly upstream source reduction strategies can be added to the mix to achieve an ecologically sustainable net level of nutrient loading.

Tasks and activities for next reporting period

Tasks for the next reporting period
Scheduled tasks for the reporting period are:

Model development:

• incorporation of 2005 field work data
• review and revision of model structure and preliminary results

Field/lab work:

• analysis of July 2005 sediment samples for denitrification rates
• final sampling of growth and survival rates in oyster and quahog plots
• removal of oysters to deep water for winter

Report production and dissemination

Work Plan for Next Reporting Period
We are now completing the analysis of sediment samples from the July 2005 field work session. Once these analysis are complete, we will incorporate the resulting denitrification rates into our bio-geophysical model and write up project results.

We hope to continue the project for one or two additional years, in part to capture the full effect of shellfish growth to market size (third growing season) on denitrification rates. We will therefore remove oysters from experimental trays by November 2005 and place them in over-winter bags in deep water in Waquoit Bay. In the process of winterizing the site, we will also conduct another round of growth/survival measurements on both oyster and quahog plots.

Concerns or difficulties
No significant difficulties are expected. Under our no-cost extension, we anticipate delivering the final project report by January 2006.

Expenditures
Expenditures to date are in line with expectations.

References
Bowen, J.L. and I. Valiela. 2001. The ecological effects of urbanization of coastal watersheds: historical increases in nitrogen loads and eutrophication of Waquoit Bay estuaries. Can. J. Fish. Aquat. Sci. 58:1489-1500.

Newell, R., T. Fisher, R. Holyoke, and J. Cornwell. 2004. Influence of eastern oysters on nitrogen and phosphorous regeneration in Chesapeake Bay, USA. In: The Comparative Roles of Suspension Feeders in Ecosystems, eds. Dame, R. and Olenin, S., NATO Science Series: IV ­ Earth and Environmental Sciences. Kluwer Academic Publishers, Dordect, The Netherlands.

Valiela, I., M. Geist, J. McClelland, and G. Tomasky. 2000. Nitrogen loading from watersheds to estuaries: verification of the Waquoit Bay Nitrogen Loading Model. Biogeochemistry 49: 277-293.